Cities serve a purpose. More segmentation, division and specialization of labor is one element of city life. The second is that among the labor element is the development of leisure and work time for thinking and creating. More inventions get developed. “Elites” develop and the elites become the controllers. Elites devise the official and accepted terms. In time the elites produce the calcification of the society the earlier generations of their class helped develop. People start to move away from the central control of the cities. Some of the inventions and mores of the city migrate with the people.
Our own society is in the process of developing the end of its cities, and the end of our society as we know it. The elites are calcifying everything, turning all politics into religion, with orthodoxy, blasphemy, and punishment for objectors increasing. They - the elites - inherited a lot, and they will destroy what their grand parents and great grand parents built.
I think you probably nailed it. The elites developed more and more power until at some point the people, who were likely more seasonal in their habitation than their European counterparts [Indians farming in spring and summer in the area of the city, and hunting in fall and winter in the outermost suburbs], realized they could just stay in the suburbs or frontier areas and be better off.